Optical fiber interconnection for computer communication applications such as clock distribution, memory and interprocessor data bus, matrix or cross-point switches offer a unique set of advantages in system architecture, package design, function, and performance. On the other hand there are some problems associated with this technology.
One of the problems is in the assembly and manufacturability of optical fiber links for interconnection, such as, tolerances on fiber alignment to the semiconductor junctions of the optoelectronic communication devices, viz. laser transmitters and photoreceivers. Arrays of fiber links into fluid-sealed semiconductor chip packages further pose problems in strain-relief at device interfaces, fan-out distribution, integrability, and spatial efficiency. Some of these known problems have been resolved by this invention.
The application of preferential crystallographic etching of V-grooves in silicon with photolithographic accuracy was taught by Crow et al., "GaAs Laser Array Source Package," OPTICS LETTERS, Vol. 1, No. 1, pages 40-42 (July 1977). His work also established the feasibility of achieving the required fiber core alignment tolerances.
U.S. Pat. No. 4,730,198 (Brown, et al.) extends the application of V-groove fiber mounting techniques, which were compatible for electrical and optical connections.
Optimizing emitter (LED or laser diode) placement relative to a fiber-optic silicon V-groove was treated by Balliet et al., in IBM Technical Disclosure Bulletin, Vol. 24, No. 2, pages 1158-1160 (July 1981), by balancing the outputs of a pair of junction diodes integrated on the undersides of the V-groove.
Methodology for preferential chemical etching of GaAs is given in Commerford and Zory, "Selectively Etched Diffraction Gratings in GaAs," APPLIED PHYSICS LETTERS, Vol. 25, No. 4, pages 208-210 (Aug, 15, 1974), and Tsang and Wang, "Profile and Groove-Depth Control in GaAs Diffraction Gratings Fabricated by Preferential Chemical Etching in H.sub.2 SO.sub.4 -H.sub.2 O.sub.2 -H.sub.2 O System" APPLIED PHYSICS LETTERS, Vol. 28, No. 1, pages 44-46 (January 1976).
Extension of fiber V-groove structure to GaAs substrates with self-aligned monolithically integrated GaA1As laser was shown by Brady et al., in IBM Technical Disclosure Bulletin, Vol. 26, No. 11, pages 5993-5995 (April 1984) to provide submicron photolithographic alignment tolerances.
Thus, it is clearly recognized that either silicon or gallium arsenide V-grooves may be used.
In U.S. Pat. No. 4,732,446, (Gipson et al.) optical fibers were embedded within the body of a printed circuit board and interfaced with discrete, lensed and beam-split chip carriers to create a simultaneous optical bus and electrical data network. Multiple printed circuit board layers, separated by aluminum heat sink plates, could be stacked and a card edge connector could form the interface to incoming data cables. Because of the multiplicity of chip carrier interfaces the modal noise and optical power losses associated with this structure can be expected to significantly exceed those of the present invention.
Conventional approaches for electrical connection include the wire bond lead or "TO-# Can" package typified in U.S. Pat. No. 4,647,148 (Katagiri) and, "tab connection" typified in U.S. Pat. No. 4,722,586, (Dodson et al.).
The present invention teaches compatible designs for interfacing external lightwave conduits into a fluid-sealed, temperature-controlled module, and, direct distribution within the module to selectable semiconductor chip positions, in either simplex or duplex fiber modes, for either bidirectional or unidirectional lightwave signals. The present invention further teaches surface connection, avoiding passage through module layers or cooling structures, and, eliminating auxiliary arrays of photonic transmitters and receivers at the module-cable edge interface, as disclosed in U.S. Pat. 4,169,001, (Kaiser).
The use of controlled collapse chip connection (C-4) with lithographically precise solder ball arrays for positioning and electrically connecting the optical pedestal to the substrate having semiconductors further distinguishes the present invention.
In the present invention, the optical pedestal and C-4 provides an integrated optical subassembly and alignment means, assuring thermal coefficient of expansion match to the substrate, optimum impedance, spatial efficiency, and reliability. The option for direct C-4 attachment to the substrate is provided for in alternate embodiments.
Further mechanical design distinctions of the present invention include the Thermal Conduction Module (TCM) - fiber optic penetration assembly, fiber guide structure, optical fiber strain-relief, optical pedestal assembly, and separability of the upper and lower half-planes of the TCM, primarily for test and repairs.